Abstract:

A software structure which when adapted in an apparatus is capable of
virtual manufacturing of transmission elements for example gear means
with chip formation, the software structure comprising a start module for
loading the source file in a main editor-file that contains the computer
program, an input module for providing input parameters that are
essential for the configuration of a product and a cutting tool, a
product design module for evolving the parameters for the manufacturing
of the product; and a virtual manufacturing module having at least three
sub-modules one each for tool generation, visualisation of machining
operation, and disassembly of the product from the machine bed.

Claims:

1. A software structure which when adapted in an apparatus is capable of
virtual manufacturing of transmission elements for example gear means
with chip formation, the software structure comprising:a start module for
loading the source file in a main editor-file that contains the computer
program;an input module for providing input parameters that are essential
for the configuration of a product and a cutting tool;a product design
module for evolving the parameters for the manufacturing of the product;
anda virtual manufacturing module having at least three sub-modules one
each for tool generation, visualisation of machining operation, and
disassembly of the product from the machine bed.

2. The software structure as claimed in claim 1, wherein the input module
is enabled to check the validity of the input data and further check the
default data.

3. The software structure as claimed in claim 1, wherein the
tool-generation sub-module creates a solid model of the tool with all the
cutting geometry for example, major cutting angles including a clearance
angle in respect of the cutter, and wherein the solid tool is enabled to
animate in the virtual environment during the cutting process.

4. The software structure as claimed in claim 1, wherein the visualisation
of machining operation sub-module is adapted to generate the product.

5. The software structure as claimed in claim 1, wherein the disassembly
sub-module is enabled to simulate the activities of dismantling the job
from the worktable in a virtual environment.

6. The software structure as claimed in claim 1, which when loaded and
operated in an apparatus enables performing the following method
steps:designing a cutting machine preferably a milling machine;forming a
blank to be configured with gear teeth;forming a cutting tool, preferably
disc type cutter adaptable to the milling machine;inputting desired data
in respect of speed of the gear, module of the gear, transmitted power,
transmission ratio, pressure angle, material of construction of the gear
and the cutter, and helix angle in case of helical gear;activating
parameters of optional modules such as material, camera, light,
animation, and render;inputting data relating to a predefined path for
chip movement; andactivitating the automatic cutting operation of the
transmission element with the input of data respecting rotational speed
of the cutter, angle of cut, blank rotation, rotational angle of the
cutter, depth of cut, and number.

8. A computer apparatus for virtual manufacturing of transmission elements
for example, gears comprising a general purpose computer interfaced with
input devices and a display device; and a software support structure as
claimed in claim 1.

9. The software structure as claimed in claim 3, wherein the visualisation
of machining operation sub-module is adapted to generate the product.

10. The software structure as claimed in claim 1, wherein the disassembly
sub-module is enabled to simulate the activities of dismantling the job
from the worktable in a virtual environment.

11. A computer apparatus for virtual manufacturing of transmission
elements for example, gears comprising a general purpose computer
interfaced with input devices and a display device; and a software
support structure as claimed in claim 7.

Description:

FIELD OF THE INVENTION

[0001]The present invention relates to virtual manufacturing of
transmission elements for example, gears. More particularly, the present
invention relates to a software structure that enables virtual
manufacturing of transmission elements for example, gears, with chip
formation.

BACKGROUND OF INVENTION

[0002]Manufacturing of the transmission elements seems to be fairly
complicated event to the person having thorough technical knowledge in
the related field. The conventional generation processes of transmission
elements for example, a gear comprising for example, forming, shaping,
hobbing etc. are usually represented in two-dimensional sketches.
However, it may be difficult to understand the complex geometries and the
manufacturing arrangement with the help of 2D models. Though this
limitation can be partially overcome using 3D solid model instead, the
development of the models using 3D solids may not always ensure the
clarity of the complex generation process of transmission elements,
unless one uses animation to represent the motion of the blank and the
cutter. This can be achieved very efficiently with the help of Virtual
Manufacturing technique.

[0003]The growing developments in virtual reality (VR) systems have
created a growing potential for applications of VR and the associated
technologies. VR involves immersion of the subject in a
computer-generated environment that looks and feels real. It is a
technology to create virtual environment on the computer screen to
simulate the physical world. The knowledge base and expertise gained from
the work in the virtual environment enables the user to apply then more
meaningfully in the real life situation.

[0004]During any manufacturing process chip formation and chip breaking
mechanism have been found to be a focus of attention for many years.
Starting with the Merchant chip formation model in 1945, many researchers
have contributed to the understanding of this area. The results of past
studies [1, 2] were based on simple cutting tools which have the same
tool geometry and cutting parameters along the cutting edge. There has
been less research on complicated cutting tools, whose geometry and
cutting parameters differ along the cutting edge. The present invention
attempts to simulate manufacturing process of transmission elements
providing special emphasis on the chip formation involved during any
cutting operation.

[0005]A host of literature is available on Virtual Manufacturing in
different areas among which some of the recent and important works are
referred below. Tesic and Banerjee have worked in the area of rapid
prototyping using Virtual Reality technologies, distillation and auto
interpretation. Balyliss et. al used the virtual reality technologies in
order to provide an outstanding 3D visualization of the object. Later G.
M. Balyliss et. al presented theoretic solid modeling techniques using
the VM tools, like VRML (Virtual Reality Manufacturing Language) and
3D-STUDIO MAX. They have used their technique to represent various
components used in automobile industry. Kimera has further enhanced the
work by representing product and process modeling as al kernel for
virtual manufacturing environment. In his work, Kimura has addressed
significant modeling issues like representation, representation language,
abstraction, standardization, configuration control, etc. Arangarasan and
Gadh used the platform of MAYA and VRML to simulate planned production
process. At Jadavpur University and Birla Institute of Technology
research work is being carried out to simulate the gear manufacturing
processes using AUTOCAD and 3D Studio Max as the platform.

[0006]A study of the state of the art and literature review reveal that
the scope of virtual manufacturing is wide open even for generation
processes of transmission elements for example, spur gear. Computer
simulation can be very effectively used to view and subsequent analysis
of different complicated manufacturing processes using the concept of
design centered virtual manufacturing.

OBJECTS OF THE INVENTION

[0007]It is therefore an object of the invention to propose a software
structure that enables virtual manufacture of transmission elements for
example, gears, with chip formation.

[0008]Another object of the invention to propose a software structure that
enables virtual manufacture of transmission elements for example, a spur
gear, which includes simulation of chip formation during the step of gear
forming.

[0009]A still another object of the invention is to propose a software
structure that enables virtual manufacture of transmission elements for
example, a spur gear, which can be implemented on a 3D-STUDIO-MAX
platform by adapting virtual tools.

[0010]A further object of the invention is to propose an apparatus capable
of adopting the software structure of the invention for virtual
manufacture of transmission elements.

SUMMARY OF THE INVENTION

[0011]While the apparatus and the software structure of the invention is
applicable for virtual manufacture of various transmission elements, for
the sake of practical demonstration of the invention, a process of gear
cutting has been described in the text. However, the present invention is
not limited to virtual manufacturing of gears only.

[0012]There are various methods of gear cutting. Each of these methods has
a field of application to which it is best adapted. The type of gear
being manufactured usually dictates the selection of the process. Since
one of the objective is to simulate the phenomenon of chip formation,
gear milling process has been chosen as the operating environment using
conventional up milling. Both spur and helical gears are generated in
virtual reality. According to the invention, the procedure followed for
virtual manufacturing of a transmission element for example, a gear, can
be summarized as under:

[0013]Spur Gear Generation

[0014]A disc type form cutter has been used for the purpose. Usually a
milling machine is designed for the same. Here the cutting cycle is made
completely automatic, including fast return of the tool and indexing of
the blank until all the teeth are generated. In this process a form
cutter passes through the gear blank to remove the material forming the
tooth gap. Adjusting the axis of the gear blank and axis of cutter
introduce the requisite depth of cut appropriately.

[0015]The desired depth of cut is achieved in number of cuts as specified
by the user in the input data. After the completion of one tooth of the
gear, the blank rotates and the cycle repeats. The process continues till
all the teeth are generated. An attempt has been made to incorporate all
the features mentioned above so as to make the software realistic and
user friendly.

[0016]Helical Gear Generation

[0017]A disc form cutter has been used for the purpose. If cutting plane
of the cutter is inclined to the vertical plane a helical gear is
generated. The same method has been used with a variation; instead of
inclining the teeth of the cutter, the cutter as a whole is inclined.
Unlike the case of spur gear, the cutting movement of the cutter is not
along the radial direction of the blank but it is inclined by the angle
equal to the helix angle as specified by the user. The cutter has only
rotational motion while other movements are imparted on the blank.

[0024]In order to clarify the process of chip formation, characteristics
of each factor are mentioned below in brief.

[0025]Type of Chip

[0026]The material of the gear dictates the type of chip being generated.
They can be segmented, continuous, continuous with built up edge or
inhomogeneous chip. [0027]1. The segmental chip are formed by a
fracture mechanism when brittle materials are cut at low cutting speeds.
[0028]2. The continuous chips are formed without a built-up edge on the
tool. This type of chips is formed during cutting of ductile materials
under steady-state conditions. [0029]3. The continuous with built up edge
(BUE) are generated under low cutting speeds where the frictions between
the chip and the rake face of the tool is resulting high temperature and
subsequent weldment of the chip to the tool face. This accumulation of
chip material is known as built-up edge. [0030]4. The inhomogeneous chips
are obtained during cutting operation of hardened and stainless steels
and titanium alloys at high cutting speeds. They are macroscopically
continuous chips consisting of narrow band of heavily deformed material
alternating with larger regions of relatively undeformed material.

[0031]Path of Chip Movement

[0032]The basic mechanism by which chips are formed during the gear
cutting is that of the deformation of the material lying in front of the
cutting edge because of the shearing action. The movement of the chip
formed is along a defined path,

[0039]The software module has been designed in such a manner that the chip
movement will be along a spline. The spline has been created by using the
equation:

θ=-(π/2-γ)

[0040]During the operation of gear cutting three chips are formed for each
tooth of the cutter. Two are flank chips and one is bottom chip. In the
simulation, it is assumed that chips are being generated independently
without interfering with one another.

[0041]Curling of Chip

[0042]As the layer becomes thicker and acquires a wedge shape as a result
of which curvature (curling) is produced. The principal factors
influencing chip curling are cutting angle, thickness of the uncut chip
(rate of feed), cutting speed, cutting fluid etc. Depending upon the
machining conditions, the chip can curl into a flat (logarithmic) spiral
or into a helix. Flat spirals are formed in case

φ=90° and γ=0.

[0043]In the machining of gears φ≠90° and γ±0
hence the chip will curl into a helix.

[0044]Due to plastic compression of the layer of metal being cut, the chip
turns out to be shorter than the part of the blank it has been cut, i.e.
L0>L. This shortening is known as longitudinal shortening and is
characterized by coefficient of contraction or cutting ratio (k) where
k=L0/L

[0045]The value of k, in general, lies between 6 and 8.

[0046]Hence the invention depicts the chip formation using the above
mentioned spline equation under the following assumptions: [0047]1. The
type of chip formed is considered to be continuous with built up edge
(BUE) as the gear material is generally ductile and the cutting speed is
also low [0048]2. The chip width is taken to be equal to the width of cut
[0049]3. The thickness is assumed to be constant throughout, and [0050]4.
The value of contraction ratio, k is assumed to be 7

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0051]FIG. 1(a)--schematically shows the movement of the gear blank and
the cutter during the cutting process according to the invention.

[0052]FIG. 1(b)--shows the rotational movement of the cutter, the other
movement being imparted on the blank.

[0069]As shown in FIG. 1(a), a disc type form cutter in a milling machine
is designed including indexing of the job (blank). The figure shows the
movement of the tool during formation of the teeth in a spur gear. FIG.
1(b) shows the rotational movement of the tool in a helical gear
generation in which other movement is imparted on the job (blank). During
the virtual manufacturing process, chip formation is a novel phenomenon
in the innovative cutting process of the invention in order to achieve
the effect of chip formation several characteristic for example, type of
chip, path of chip movement, curling of chip, and chip construction are
taken into consideration.

[0070]FIG. 2(a) shows the generation of chip during the cutting process.
According to the invention, the path of chip movement has been defined
along a spline which has been shown in FIG. 2(b). The spline has been
created by adapting a relationship of, θ=-(π/2-γ), where
Vc is the chip velocity, v is the cutting speed, θ is chip movement
angle, φ is shear angle, ψ is Rack angle, t1 is width of
cut, and t2 is chip width. The type of chip formed during the
cutting has been discussed hereinabove which generally relates to type of
material cut, the tool designed, and rotational speed of the tool
including the job (blank) movement. FIG. 2(c) shows the type of chips for
example, flank chips and bottom chip generating during gear-cutting.

[0071]FIG. 2(d) shows the `curling of chips` which depends on cutting
angle, rate of feed, cutting speed, cutting material, and cutting fluid
used. The curling can be in a logarithmic spiral, or a helix shape.

[0072]FIG. 2(e) shows the phenomenon of `chip construction`, which can be
described as `shortening` which results due to plastic compression of the
layer of metal which is cut. Accordingly, the chip turns out to be
shorter than the part of blank cut.

[0073]The present invention can be implemented in a general-purpose
computer apparatus having an operating system with hardwares like storage
devices in the form of Read only memory (ROM), and random access memory
(RAM) a display device interfaced with the processor, several input
devices for example keyboard, mouse. The invention can also be
implemented in a special-purpose computer with appropriate hardwares
capable of running and operating the software of the invention.

[0074]The software module is written in such a way that the user is
guided, with the help of user friendly screens, stepwise from creation of
the gear, cutter and the various input parameters to the final output in
form of Frames or a movie clip. In the final output the user not only
visualizes the gradual forming of gear tooth but also gets a realistic
view of chip formation and dispersion. This makes the output close to
actual machining in a milling machine. The entire system is developed in
modular form. They are: start module; Input Module; Optional Module and
Virtual Manufacturing Module. A brief description of each of these
modules is mentioned below.

[0075](a) Start Module

[0076]This module loads the source-file in the main editor-file that
contains all the programs developed in MAX--Script language using a
particular code. When 3D-STUDIO MAD is accessed the interface and is
displayed at first, it does not contain all the tool bars. Hence it is
required to customize the interface so that all the tool bars are loaded.
It is advisable to open and load through the file menu of the Max-Script
listener which is one of the most important display unit of 3D-STUDIO
MAX. When an attempt is made to evaluate a max-script program file, the
processing and the outcome are displayed at each level of execution of
the program and flash an error message to the user.

[0077](b) Input Module

[0078]The various design parameters are evaluated first and data are
entered through the input dialogue window specially created by max script
language has to be filled in. The various parameters have been assigned
with a predefined upper and lower limit to make the module more user
friendly. If the user gives any erroneous data the module would start
giving warning message and would not proceed further till all the dta are
properly filled up and none of the compulsory parameters omitted. A
sample input dialogue windows are shown in FIG. 8.

[0079]In order to manufacture a gear the user is required to provide
certain essential parameters e.g. [0080]1. Speed of the gear [0081]2.
Module of gear [0082]3. Transmitted power [0083]4. Transmission ratio
[0084]5. Pressure angle [0085]6. Material of construction of the gear and
cutter [0086]7. Helix angle in case of the helical gear [0087]8. Left
handed or right handed gear

[0088]There are certain optional data, for example the depth of cut, the
number of cut, precision of the gear etc. Each parameter requires some
predetermined value which the user must enter before proceeding further.
Moreover if the user wants to modify any one or more parameters, the
program can be recalled and the changes can be made resulting automatic
up gradation of the product. This practice is almost impossible in an
actual machine and thus saves time and cost.

[0089](c) Optional Module

[0090]In order to provide a realistic view of the gear cutting operations,
a few optional modules have been introduced. They are named as material,
camera, light, animation and render. The scope of each optional module is
mentioned below:

[0091]Material

[0092]Colour is probably the simplest material property and the easiest to
identify. Within the Material Editor, there are several different colour
swatches or effects that control different aspects of the object's
colour. The following list describes the types of colour swatches that
are available for simple materials:

[0093]Ambient: Defines an overall background lighting that effects all
objects in the scene, including the colour of the object when it is in
the shadows. This colour can be locked to the diffuse colour so that they
are changed together.

[0094]Diffuse: The surface colour of the object surface in normal full
light. The normal colour of an object is typically defined by its Diffuse
colour.

[0095]Specular: The colour of the highlights where the light is focused on
the surface of a shiny material.

[0096]Self-illumination: The colour that the object glows from within.
This colour takes over any shadows on the object.

[0097]Filter: The transmitted colour caused by light shining through a
transparent object.

[0098]Reflect: The colour reflected by a ray trace material to other
objects in the scene.

[0099]Luminosity: Caused an object to glow with the defined colour. It is
similar to Self-Illumination colour but can be independent of the diffuse
colour.

[0100]Opacity and transparency: Opaque objects are objects that cannot see
through, such as metals. Transparent objects, on the other hand, are
objects that can be seen through, like glass. The software materials
include several controls for adjusting these properties, including
Opacity and several Transparency controls. Opacity is the amount that an
object refuses to allow light to pass through it. An object with 100
percent opacity is completely transparent, and an object with opacity of
100 percent doesn't let any light through. Transparency is the amount of
light that is allowed to pass through an object. Because this is the
opposite of opacity, transparency can be defined by the opacity value.
Several options enables the user to control transparency, including
Falloff, Amount, and Type. A typical material sheet is shown in FIG.
9(a).

[0101]Reflection and refraction: Shiny objects like polished gear reflect
their surroundings. Refraction is the bending of light as it moves
through a transparent material. The amount of refraction that a material
produces is expressed as a valve called the Index of Refraction. The
Index of Refraction is the amount that light bends as it goes through a
transparent object. The default Index of Refraction value is 1.0 for
objects that don't bend light at all. By defining a material's reflection
values, the user can control how much reflection is required for his
setup. A gear, for example, reflects the images of chips, but a chip
won't reflect at all.

[0102]Camera

[0103]There are two types of cameras that the user can create namely a
Free camera and a Target camera. Camera objects are visible as icons in
the screen, but they aren't rendered. The camera icon looks like a box
with a smaller box in front of it, which represents the lens or front end
of the camera. Both the Free and Target camera types can include a cone
that shows where the camera is pointing.

[0104]Free Camera

[0105]The Free camera object offers a view of the area that is directly in
front of the camera and is the better choice if the camera will be
animated. The single parameter for Free cameras defines a Target
Distance--the distance to an invisible target about which the camera can
orbit.

[0106]Target Camera

[0107]A Target camera always points at a controllable target point some
distance in front of the camera. Target cameras are easy to aim and are
useful for situations where the camera won't move. The user can make
modifications in the camera position and property. A typical modified
panel's parameters rollout for the camera is shown in FIG. 9(b).

[0108]Light

[0109]Lighting plays a critical part of any virtual manufacturing process.
Understanding the basics of lighting can make a big difference in the
overall virtual perspect of the rendered scenes. The software has an
option of using two types of lighting: natural light or artificial light.
When lighting a scene, not relying on a single light is best. The
software includes one key light and several secondary lights. A spotlight
has been used for the main key light. It is positioned in front of and
slightly above the gear cutter arrangement, and it casts shadows, because
it is the main shadow-casing light in the scene. The secondary lights
fill in the lighting gaps and holes. The position of these are at floor
level on either side of the gear and cutter, with the intensity set at
considerably less than the key light and set to cast no shadows. FIGS.
9(c) and 9(d) show a sample lightening parameters that are generally
played to fetch a good view of the cutting process.

[0110]Animation

[0111]The user can set several options including the Frame Rate. Frame
rate provides the connection between the number of Frames and time. It is
measured in Frame per second. The options include standard Frame rates
including NTSC (National Television Standards Committee, around 30 Frames
per second), Film (around 24 Frames per second), and PAL (Phase Alternate
Line, used by European countries around 25 Frames per second), or user
can decide on the Frame rate based on his choice as shown in FIG. 9(e).

[0112]The Time Display section allows to set time on the Time Slider. The
options include Frames, SMPTE (Society of Motion Picture Technical
Engineers), Frame: Ticks or MM:SS:Ticks (Minute and Seconds) SMPTE is a
standard time measurement used in video and television. A Tick is 1/4800
of a second.

[0113]Render

[0114]Render is the doorway to the final output. Here the user can
manipulate the rendering operation using the following dialog box. A
typical dialogue box looks like FIG. 9(f).

[0115]The Render Scene dialog box includes options the output options such
as which Frames to render and the final image size can be specified.

[0116]The Environment dialog box includes options the environment settings
such as a background colour or image, global lighting settings, and
atmospheric effects such as Combustion, Fog, and Volume Lights can be
adjusted.

[0118]The Advanced Lighting control panel where the settings for the Light
Tracer, Radiosity, Exposure Control, and Lighting Analysis tools are
located.

[0119](d) Virtual Manufacturing Module

[0120]Virtual manufacturing gives life to already created stationary
objects using the input module discussed earlier. In other words, it
simulates the dynamic behaviour of gear cutting which is created as a
series of still pictures. The still pictures, known as Frames (FIGS. 3,
4, 5, 6) are first generated with a little change of position of the gear
blank and cutter from the previous one. When these Frames are displayed
in proper sequence at successive interval, they create the impression of
gear cutting, blank movement, cutter movement etc. For creating a proper
illusion of animation, as discussed in the special module, developer must
have thorough understanding of the max-script programming environment of
3D Studio Max. The animated output is stored in the hard disc and can be
played using suitable media player.

[0121]A few important features of the software module are highlighted
below.

[0122]The up and down motion with simultaneous forward movement of the
gear blank and the rotating cutter creates the impression of cutting of a
tooth on the blank. A large number of such Frames are generated by the
software to depict the different stages of material removal from the gear
blank to the final finish. The upward motion of the blank corresponds to
the cutting stroke, the downward motion represents the idle stroke while
positioning of the cutter under the blank illustrates the depth of cut.

[0123]A few important frames are shown in FIGS. 3-6. The Frame 1, as shown
in FIG. 3 illustrates the beginning of the operation and the next Frame
(Frame 2) shows the position at the end of the cutting action of the
tooth. Such successive Frames illustrate the disengagement of the cutter,
withdrawal of the blank, indexing, and positioning of the blank by
rotation to its next place, reengagement of the cutter when the cutting
of the next tooth begins. When all these Frames are shown one after
another in their sequential order, the observer gets the impression of
virtual manufacturing of the gear.

[0124]FIG. 4 exhibits a close up view of the chip formation during the
cutting operation of the gear blank. The similar method is followed to
simulate the cutting operation of helical gear as well. A few selected
Frames are shown in FIGS. 5 and 6. The software module further provides
movie files where the Frames can be moved with a projection rate suitable
to give a clear demonstration of the virtual manufacturing process. In a
movie it is not possible to change the viewing direction and the target
position. In the present invention user can select either of them (or
both) as per his choice and hence can have better understanding of the
operational principle of gear cutting by form tools.

[0125]The invention has the advantage of creating movie files in which a
user can control projection of Frame rates. The slow motion projection is
very helpful for demonstration purpose as well.

[0126]The present invention provides the entire procedure of gear
manufacture using a form cutter in a virtual environment. The software
support structure is developed in a modular form to accommodate
additional features of gear generation without disturbing the original
software. In addition it includes the aspect of chip formation during
gear cutting operation making it more realistic. The apparatus has the
capacity to create movie files for a better understanding of a,
otherwise, complex manufacturing process capturing the phenomenon of chip
formation as well. The invention automatically disables the insertion of
inadequate data by giving a warning message and indicating the necessary
corrective measures.

[0127]The invention also helps the user to have a clear preconception of
the actual gear that will be manufactured on the given data. The user can
also change the design to suit the requirement, by changing the relevant
parameters. The invention can be a very efficient learning aid for those
who want to have proper understanding of gear manufacturing operation by
form tool.